Haiqing Chang

Relationship between soluble microbial products (SMP) and effluent organic matter (EfOM): Characterized by fluorescence excitation emission matrix coupled with parallel factor analysis

Effluent organic matter (EfOM) originating from wastewater treatment plant (WWTP) is of significant concern, as it not only influences the discharge quality of WWTP but also exerts a significant effect on the efficiency of the downstream advanced treatment facilities. Soluble microbial products (SMP) is a major part of EfOM. In order to further understand the relationship between soluble microbial products (SMP) and EfOM, and in turn, to propose measures for EfOM control, the formation of SMP and EfOM in identical activated sludge sequencing batch reactors (SBR) with different feed water was investigated using fluorescence excitation and emission spectroscopy matrix coupled with parallel factor analysis (EEM-PARAFAC) as well as other organic matter quantification tools. Results showed that EfOM contained not only SMP but also a considerable amount of allochthonous organic matter that derived not merely from natural organic matter (NOM). Four components in EfOM/SMP were identified by EEM-PARAFAC. Tyrosine-like substances in EfOM (Component 3, λex/em=270/316 nm) were mainly originated from utilization associated products (UAP) of SMP. Tryptophan-like substances (Component 2, λex/em=280/336 nm) as well as fulvic-like and humic-like substances in EfOM (Component 1, λex/em=240(290)/392 nm and Component 4, λex/em=260(365)/444 nm) were majorly derived from the refractory substances introduced along with the influent, among which Component 2 was stemmed from sources other than NOM. As solid retention time (SRT) increased, Component 2 and polysaccharides in SMP/EfOM decreased, while Component 4 in SMP increased.

Impact of dataset diversity on accuracy and sensitivity of parallel factor analysis model of dissolved organic matter fluorescence excitation-emission matrix.

Parallel factor (PARAFAC) analysis enables a quantitative analysis of excitation-emission matrix (EEM). The impact of a spectral variability stemmed from a diverse dataset on the representativeness of the PARAFAC model needs to be examined. In this study, samples from a river, effluent of a wastewater treatment plant, and algae secretion were collected and subjected to PARAFAC analysis. PARAFAC models of global dataset and individual datasets were compared. It was found that the peak shift derived from source diversity undermined the accuracy of the global model. The results imply that building a universal PARAFAC model that can be widely available for fitting new EEMs would be quite difficult, but fitting EEMs to existing PARAFAC model that belong to a similar environment would be more realistic. The accuracy of online monitoring strategy that monitors the fluorescence intensities at the peaks of PARAFAC components was examined by correlating the EEM data with the maximum fluorescence (Fmax) modeled by PARAFAC. For the individual datasets, remarkable correlations were obtained around the peak positions. However, an analysis of cocktail datasets implies that the involvement of foreign components that are spectrally similar to local components would undermine the online monitoring strategy.

Towards a better hydraulic cleaning strategy for ultrafiltration membrane fouling by humic acid: Effect of backwash water composition

As a routine measurement to alleviate membrane fouling, hydraulic cleaning is of great significance for the steady operation of ultrafiltration (UF) systems in water treatment processes. In this work, a comparative study was performed to investigate the effects of the composition of backwash water on the hydraulic cleaning performance of UF membranes fouled by humic acid (HA). Various types of backwash water, including UF permeate, Milli-Q water, NaCl solution, CaCl2 solution and HA solution, were compared in terms of hydraulically irreversible fouling index, total surface tension and residual HA. The results indicated that Milli-Q water backwash was superior to UF permeate backwash in cleaning HA-fouled membranes, and the backwash water containing Na(+) or HA outperformed Milli-Q water in alleviating HA fouling. On the contrary, the presence of Ca(2+) in backwash water significantly decreased the backwash efficiency. Moreover, Ca(2+) played an important role in foulant removal, and the residual HA content closely related to the residual Ca(2+) content. Mechanism analysis suggested that the backwash process may involve fouling layer swelling, ion exchange, electric double layer release and competitive complexation. Ion exchange and competitive complexation played significant roles in the efficient hydraulic cleaning associated with Na(+) and HA, respectively.

A pilot-scale study of a powdered activated carbon-membrane bioreactor for the treatment of water with a high concentration of ammonia

A submerged, powdered activated carbon-membrane bioreactor (PAC-MBR) at a pilot-scale (2.2 m3 h−1) was used to treat surface water with a high concentration of ammonia (~2.64 mg L−1) and a low alkalinity. The ammonia removal efficiency and its influencing factors (i.e., temperature, alkalinity and aeration mode) were systematically investigated. The results showed that the PAC-MBR could effectively remove a high concentration of ammonia when the temperature was higher than 20 °C, and exhibited good resistance to ammonia fluctuation (fluctuation range: 1–3 mg L−1). The ammonia removal capacity of the PAC-MBR exponentially decreased as the temperature decreased over a temperature range from 13 °C to 24 °C. Alkalinity became the limiting factor when the temperature exceeded 24 °C, and ammonia removal linearly increased as the alkalinity increased. Moreover, intermittent aeration at an appropriate aeration interval was proven to provide enough oxygen for biological nitrification. Furthermore, the foulants attached on the membrane surface could also contribute to the ammonia removal during the filtration. The PAC-MBR process could serve as a potential option to address elevated levels of ammonia under steady and transient state operation.

Correlating ultrafiltration membrane fouling with membrane properties, water quality, and permeate flux

AbstractThe effect of membrane properties, feed water quality, and permeate flux on ultrafiltration (UF) membrane fouling was systematically investigated. Fouling tests were carried out with three types of commercially available UF membrane and a variety of influents. The membrane fouling was assessed by the normalized fouling rate (F500). The results showed that the PVDF membrane with smaller contact angle was more resistant to membrane fouling than the PVC membrane. As for feed water parameters, significant correlations were observed between turbidity, total organic carbon, UV254, fluorescence intensity, and membrane fouling rates using Pearson Correlation Analysis. This was especially true for hydraulically irreversible fouling rate (Firr). Moreover, significant correlations between permeate fluxes and membrane fouling rates were observed. With these correlations, the critical flux and critical flux for irreversibility were calculated. It was found that the critical flux is strongly depended on feed wa...